Modular energy storage system

Abstract

The invention discloses a modular energy storage system, which is characterized in that n arc magnet modules are connected end to end to form an annular superconducting magnet, each arc magnet module is connected in parallel with a direct current power grid through a direct current bidirectional current source power converter, and the power converter controls voltage and current sharing of each arc magnet module; generating equal magnetic fluxes and superposing the magnetic fluxes in the arc direction; the power converters adopt bidirectional current source two-level topology to reduce device current stress and reduce bus current ripples, a phase shift control strategy is adopted between the power converters, current and total magnetic flux ripples are effectively reduced, superconducting magnet alternating current loss is reduced, the efficiency of a superconducting system is improved, and the service life of the superconducting system is prolonged. The system can realize high-efficiency and high-power rapid conversion of electric energy and magnetic energy, and can be applied to energy conversion occasions such as novel power grids and ship comprehensive power system machines.

Description

Technical Field

[0001] The present invention belongs to the field of superconducting application, power electronics, electrical engineering and electric energy new technology, and relates to a high-efficiency, large-capacity and fast-response superconducting energy storage technology, and specifically relates to a modular energy storage system. Background Art

[0002] As a new type of material with excellent electromagnetic properties and great application potential, superconducting materials have the advantages of low conductive loss and high current density. The superconducting magnetic energy storage system can realize the rapid conversion of electrical energy and magnetic energy, achieve millisecond-level power response, and can effectively improve the quality of electric energy and the stability of the power system. The superconducting energy storage system is an energy storage device that uses superconducting magnets to store energy in the power grid in the form of electromagnetic energy, and returns electrical energy to the power grid or for other purposes when needed. It is essentially an inductive energy storage technology, consisting of energy storage magnets, converters, constant temperature dewars, cryogenic refrigeration devices, quench protection devices, monitoring systems, etc.

[0003] The superconducting magnet is the core component of the superconducting magnetic energy storage device, and its stability is related to whether the entire device can operate safely. Superconducting energy storage magnets can be made of high-temperature superconducting materials or low-temperature superconducting materials. The structural form of superconducting magnets can be annular, parallel multi-solenoid and single-solenoid: the single-solenoid structure is simple and easy to process and manufacture, but it has a large leakage magnetic field; the parallel multi-solenoid leakage magnetic field is small, but its energy storage density is very small; the annular energy storage magnet uses a medium amount of wire, and the tightly coupled structure constrains the magnetic field inside the annular coil, and the magnet leakage magnetic field is very small. The annular structure is the first choice for large-capacity energy storage magnets, but high power requires the magnet to withstand higher voltages, which brings challenges to low-temperature thermal insulation.

[0004] The cooling methods and cooling structures of magnets include immersion cooling, steam cooling, and conduction cooling. Conduction cooling does not require cryogenic liquid or steam, but instead conducts the heat of the magnet to the refrigerator through metal cooling materials. It has a compact structure and is easy to maintain. However, the introduction of cooling metal structural parts also brings about problems of low-temperature insulation and eddy current loss, which may limit the power output of the energy storage magnet and reduce the energy storage efficiency.

[0005] On the other hand, due to the existence of pinning centers in high-temperature superconducting materials, when a changing current is applied to the superconductor, the Lorentz force has to overcome the pinning force to do work, generating heat energy, which is called AC loss. AC loss will have an adverse effect on high-temperature superconductors that need to maintain a low-temperature working environment: it will not only increase the cooling cost of superconducting magnets, but also cause the magnet temperature to rise and the critical current to decrease, affecting the performance and stability of high-temperature superconducting magnets.

[0006] Since the energy storage element on the DC side of superconducting energy storage is an inductor, it is appropriate to adopt a current source converter topology, which can simplify the converter structure and improve the charging / discharging efficiency and safety. In addition to the advantages of the traditional two-level current source converter, the multi-level current source converter also has the advantages of small switching stress of a single device, large output capacity, and small harmonic content of the output waveform. It is particularly suitable for low voltage and high current occasions. In addition, with the development of switching devices with reverse blocking capability (such as integrated gate commutated thyristors), multi-level current source converters have ushered in new opportunities and have good application prospects and development trends. However, the bidirectional multi-level current source converter and its multi-objective coordinated control with modular energy storage magnets increase the technical difficulty of system development, and its development is restricted.

[0007] In principle, superconducting energy storage systems based on high-temperature superconducting materials have the advantages of low operating losses, large working capacity, and small device size. However, in practice, these advantages will be offset by refrigeration costs, and a considerable part of these costs comes from lead losses, mainly including conductive losses and heat leakage losses, which limits their application.

[0008] In summary, the increase in the capacity of superconducting energy storage systems is constrained by the problem that multiple objectives such as efficiency, power, insulation, and cooling of energy storage systems are difficult to be compatible. In particular, the increase in control dimension and the complexity of control strategies have increased the technical difficulty of system development, and its development has been restricted. Analyzing this and seeking solutions is both theoretically meaningful and practically valuable. Summary of the invention

[0009] The purpose of the present invention is to propose a modular energy storage system: design a new modular energy storage magnet, reduce the voltage of the unit energy storage magnet, reduce the difficulty of low-temperature insulation design of the conduction cooling magnet, and realize system redundancy and fault tolerance; design a new current source converter, reduce the switching stress of a single device, reduce the ripple content of the output waveform, reduce the AC loss, and be suitable for low voltage and high current, and realize high efficiency and high power; through the coordinated control of the modular energy storage magnet and the converter, further reduce the ripple content of the output waveform, reduce the AC loss, improve efficiency, and reduce refrigeration requirements; reduce the leads across the environment, fundamentally avoid unnecessary lead losses, and improve the economy of superconducting application technology, so as to realize efficient, safe, stable and rapid operation of a high-power superconducting energy storage system.

[0010] The technical solution adopted by the present invention to solve the technical problem is: a modular energy storage system adopts superconducting energy storage, including a ring-shaped superconducting magnet formed by connecting n unit arc-shaped magnet modules end to end on the circumference, the arc of the arc-shaped magnet module is 2π / n, 2≤n≤10, each arc-shaped magnet module is connected in parallel to the bus of the DC power grid through its own independent DC bidirectional current source power converter, and the charging and discharging current of the arc-shaped magnet module is controlled to be equal to reduce the voltage pressure of the magnet; the power converter controls the equalization of voltage and current of each arc-shaped magnet module, generates equal magnetic flux and superimposes it in the direction of the arc, each power converter has the function of serving as a backup for each other, and after a unit module circuit fails, the remaining unit modules can continue to operate in fault-tolerant redundancy, thereby improving the reliability of the energy storage system; the power converter adopts a two-level topology, reduces the device current stress, reduces the bus current ripple, and the power switch tube T e The emitter of the diode D e The negative electrodes are connected in series, marked as connection point E, forming bridge arm Q e , power switch tube T f The collector of the diode D f The positive electrodes are connected in series, marked as connection point F, forming a bridge arm Q f , connection points E and F are connected to the two ends of the arc magnet module respectively, and the bridge arm Q e With bridge arm Q f Connected in parallel to the DC bus support capacitor C, the bridge arm Q e Upper power switch tube T e The collector is connected to the positive bus P, and the bridge arm Q e Upper diode D e The positive pole is connected to the negative busbar N, and the bridge arm Q f The emitter of the upper power switch tube Tf is connected to the negative bus N, and the bridge arm Q f Upper diode D f The negative pole is connected to the positive bus P.

[0011] Furthermore, the arc magnet module is mainly composed of a superconducting coil, an inner ring, an outer ring, a radial support assembly, a cooling plate, a supporting side plate, a current lead assembly and a low-temperature glue.

[0012] Furthermore, the superconducting coil is a double-pancake coil wound on an inner ring, with a transition fit between the superconducting coil and the inner ring, the outer ring is sleeved on the outside of the superconducting coil, with a gap fit between the two, the gap between the outer ring and the superconducting coil is filled with a superconducting tape, and a radial support assembly is sleeved on the outside of the outer ring, with a transition fit between the two, the cold conduction plates are respectively located on both sides of the superconducting coil, and are fixedly connected to the inner ring and the radial support assembly by bolts, the support side plates are located on the outside of the cold conduction plates, and are fixedly connected to the inner ring and the radial support assembly by bolts, and the current lead assembly is located in the upper middle part of the magnet unit and is fixed on the radial support assembly.

[0013] Furthermore, the two-level power converter adopts a closed-loop control strategy to control the charging and discharging state of the arc-shaped magnetic module: the power switch tube T e Drive pulse trigger, power switch tube T e Turn on, power switch tube T f Drive pulse trigger, power switch tube T f Turn on, the arc magnet module is charged; the power switch tube T e Drive pulse trigger, power switch tube T e Turn on, power switch tube T f Drive pulse blocked, power switch tube T f Blocking, diode D e Blocking, diode D f Turn on, arc magnet module continues current; power switch tube T e Drive pulse blocked, power switch tube T e Blocking, power switch tube T f Drive pulse trigger, power switch tube T f Conducting, diode D e Conducting, diode D f Blocking, arc magnet module continuous current; power switch tube T e Drive pulse blocked, power switch tube T e Blocking, power switch tube T f Drive pulse blocked, power switch tube T f Blocking, diode D e 、Diode D f Turn on, the arc magnet module discharges.

[0014] Furthermore, the arc magnet module current adopts closed-loop control, and the regulator realizes fast tracking and error-free regulation of the charge and discharge current, and maintains the current balance of each module: The reference instruction is used to output the absolute value of the signal through the PI current regulator as the common reference modulation wave of each converter. D , each power switch tube is turned on and off according to the multi-level DC pulse width modulation strategy.

[0015] In the modular energy storage system, the power switch tube adopts a multi-level carrier phase-shift pulse width modulation strategy, and generates a PWM wave to control each group of power units respectively by comparing a plurality of triangular carriers with the same amplitude and phase shift, and then superimposes them to form a multi-level PWM waveform.

[0016] In the modular energy storage system, each power converter, i.e., power converter Ck, k∈{1, ..., n}, adopts a phase shift control strategy, which effectively reduces the total magnet synthetic flux ripple, reduces the arc magnet module induced potential and current ripple, and reduces the superconducting magnet AC loss; reduces the bus current ripple, and the power converters C1, C n Each cluster triggers a pulse sequence, shifting the phase by 2π / n within a switching cycle T. The converter modules C1 and C n Each cluster of trigger pulse sequences is delayed by T / n in sequence.

[0017] Furthermore, the power switch tube T e , T f It is a reverse-resistance switching device with reverse blocking capability but no reverse conducting capability; or it is a reverse-conducting switching device with reverse conducting capability and a diode connected in series in the forward direction at the emitter.

[0018] Furthermore, the switching device may be one of a power transistor GTR, an insulated gate bipolar transistor IGBT, an integrated gate commutated thyristor IGCT, and a metal oxide semiconductor field effect transistor MOSFET.

[0019] The beneficial effects of the present invention are as follows: the present invention adopts a combination of multiple arc-shaped magnet modules to form an annular superconducting magnet, each arc-shaped magnet module is connected in parallel to the DC power grid through its own independent power converter, reducing voltage stress; the power converter adopts a bidirectional current source two-level topology, reducing device current stress and bus current ripple, and a phase shift control strategy is adopted between each power converter, effectively reducing current and total magnetic flux ripple, and reducing superconducting magnet AC loss; the converter current sharing / shunting inductor adopts superconducting materials, reducing losses and improving the efficiency of the superconducting system. The annular superconducting magnet can realize the rapid conversion of high-efficiency and high-power electrical energy and magnetic energy, and can be applied to energy conversion occasions such as new power grids and integrated ship power systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of the overall structure of the present invention; Figure 2 It is a partial cross-sectional view of the annular superconducting magnet of the present invention; Figure 3 Schematic diagram of three traditional superconducting magnet structures; Figure 4 It is a schematic structural diagram of the annular superconducting magnet of the present invention; Figure 5 A partial cross-sectional view of the arc-shaped magnet module of the present invention; Figure 6 is an exploded schematic diagram of the arc magnet module; Figure 7It is a schematic diagram of the structure of the arc-shaped magnet module cooling plate and supporting side plate; Figure 8 The inner ring and outer ring structure of the present invention and their relationship with the superconducting coil; Fig. 9 This is a structural diagram of the radial support assembly of the present invention; Fig.10 This is a diagram of the cooling plate structure and its fixing structure of the present invention; Fig.11 The supporting side plate structure and its installation method of the present invention; Fig.12 It is a structural diagram of the current lead assembly of the present invention; Fig.13 is a schematic structural diagram of a power converter of the present invention; Fig.14 It is a bidirectional current source multi-level energy storage power converter power device; Fig.15 A phase shift control strategy is adopted between power converters; Fig.16 The current waveform adopts phase shift control strategy between magnet modules.

[0021] The reference numerals of the figures are: 01 - superconducting coil, 02 - inner ring, 03 - outer ring, 04 - radial support assembly, 05 - cooling plate, 06 - support side plate, 07 - current lead assembly. DETAILED DESCRIPTION

[0022] The present invention is further described in detail with reference to the accompanying drawings and embodiments as follows.

[0023] Reference Figure 1 As shown, the present invention discloses a current-type energy conversion system, which uses superconducting energy storage. The system uses n arc-shaped magnet modules, 2≤n≤10, and each arc-shaped magnet module has a radian of 2π / n. They are combined on the circumference to form a circular magnet as a whole. The tightly coupled structure constrains the magnetic field inside the circular coil, and the magnetic leakage field is very small. Each arc-shaped magnet module is connected in parallel to the busbar of the DC power grid through its own independent DC bidirectional current source power converter. The arc-shaped magnet module controls each arc-shaped magnet module to balance voltage and current, generate equal magnetic flux, and superimpose in the arc direction, such as Figure 2 shown.

[0024] The structure of conventional superconducting magnets is Figure 3 As shown in the figure, a is a single solenoid, b is a multi (quadruple) solenoid, and c is a ring magnet. Different from the traditional superconducting magnet structure, the arc of the arc magnet module of the present invention is 2π / n, 2≤n≤10, as shown in the figure. Figure 4 and Figure 5As shown in the figure, the tightly coupled structure constrains the magnetic field inside the toroidal coil, and the magnetic leakage field is very small; the power converter controls the voltage and current of each arc-shaped magnet module, generates equal magnetic flux and superimposes it in the arc direction, and each power converter has the function of mutual backup. After a unit module circuit fails, the remaining unit modules can continue to operate with fault tolerance and redundancy, which improves the reliability of the energy storage system. The converter shunt inductor is made of superconducting material and is integrated with the superconducting magnet into a cryostat dewar, reducing lead loss.

[0025] Reference Figure 6 As shown, the arc magnet module is mainly composed of a superconducting coil 01, an inner ring 02, an outer ring 03, a radial support assembly 04, a cold plate 05, a support side plate 06, a current lead assembly 07 and a low-temperature glue. The structure of the cold plate 05 and the support side plate 06 is as shown in FIG. Figure 7 shown.

[0026] The superconducting coil 01 is a double-pancake coil, which is wound on the inner ring 02, and the two are in a transition fit state; the outer ring 03 is sleeved on the outside of the coil, and the two are in a gap fit, and the gap is filled with superconducting tape; the radial support assembly 04 is sleeved on the outside of the outer ring 03, and the two are in a transition fit; the cold plate 05 is located on both sides of the superconducting coil 01, and is fixedly connected to the inner ring 02 and the radial support assembly 04 by bolt connection; the support side plate 06 is located on the outside of the cold plate 05, and is fixedly connected to the inner ring 02 and the radial support assembly 04 by bolt connection; the current lead assembly 07 is located in the upper middle part of the magnet unit, and is fixed on the radial support assembly 04; after the entire arc magnet module is assembled, the low-temperature glue is filled and cured by a room temperature vacuum impregnation process. In order to reduce eddy current loss, the inner ring 02, the outer ring 03 and the support side plate 06 are all made of non-metallic composite materials, and the cold plate 05 is made of copper material, which is located on both sides of the superconducting coil 01.

[0027] The inner ring 02 and the outer ring 03 are both made of composite materials. Their structures and their assembly relationship with the superconducting coil 01 are shown in the figure. Figure 8 The inner ring 02 is a stepped structure, and the superconducting coil 01 is wound on the inner ring 02; the outer ring 03 is a circular ring structure, which is sleeved outside the superconducting coil 01 and is used to withstand the electromagnetic force of the superconducting coil 01 radially outward.

[0028] The radial support assembly 04 is located outside the outer ring 03 and is mainly composed of an aluminum alloy frame, a composite material tie rod and a pressure block, such as Fig. 9 As shown. The radial support assembly 04 is mainly used to support and fix the arc magnet module, and is connected to the external cooling member. In order to reduce the eddy current loss of the aluminum alloy frame, it is divided into two parts, connected by a composite material tie rod, and pressed with a pressing block, which can reduce the eddy current loss of the frame and enhance the shrinkage consistency of the aluminum alloy frame and the outer ring 03.

[0029] The magnet unit cold conduction plates 05 are located on both sides of the superconducting coil 01 and are used for heat conduction of the superconducting coil 01. The cold conduction plates 05 are made of copper and have the following structure: Fig.10 As shown. Considering that the cold plate 05 is in a relatively large magnetic field area, eddy current loss will be generated during the charging and discharging process, the cold plate 05 is cut to reduce the eddy current loss generated by the cold plate 05. The cold plate 05 is fixedly connected to the radial component and the inner ring 02 respectively by bolt connection.

[0030] The supporting side plates 06 are made of non-metallic composite materials. The two supporting side plates 06 are installed on both sides of the superconducting coil 01. The external dimensions are consistent with the cold plate 05 and they are installed in alignment with the cold plate 05. On the one hand, the cold plate 05 and the superconducting coil 01 can fit tightly together. On the other hand, the lateral strength of the entire magnet unit can be enhanced. Considering that the strength of composite materials and aluminum alloys is not high, a stainless steel screw sleeve with internal threads is embedded to achieve threaded connection. The external structure and installation method of the magnet unit supporting side plate 06 are as follows: Fig.11 shown.

[0031] In order not to damage the integrity of the composite material outer ring 03, the current lead assembly 07 of the superconducting coil 01 is Fig.12 In the structure shown, the outermost turn of the superconducting coil 01 is led out to the upper end of the magnet unit, and the external lead is in a horizontal state to facilitate the series connection between adjacent magnet units. The current lead assembly 07 is mainly composed of an epoxy plate, an oxygen-free copper plate and a superconducting broadband. The superconducting broadband is overlapped with the outermost turn of the superconducting coil 01 and welded to the oxygen-free copper plate. The oxygen-free copper plate is fixed to the epoxy plate by bolts, and the epoxy plate is fixed to the radial support assembly 04 and the outer ring 03 by bolts. The magnet unit is provided with two sets of current lead assemblies 07, which are aligned and fixed to the upper part of the magnet unit.

[0032] The DC bidirectional current source power converter adopts a two-level topology, which reduces the device current stress and the bus current ripple. Fig.13 As shown. Power switch tube T e The emitter of the diode D e The negative electrodes are connected in series, marked as connection point E, forming bridge arm Q e , power switch tube T f The collector of the diode D f The positive electrodes are connected in series, marked as connection point F, forming a bridge arm Q f , connection points E and F are connected to the two ends of the arc magnet module respectively, and the bridge arm Q e With bridge arm Q f Connected in parallel to the DC bus support capacitor C, the bridge arm Q e Upper power switch tube T eThe collector is connected to the positive bus P, and the bridge arm Q e Upper diode D e The positive pole is connected to the negative busbar N, and the bridge arm Q f The emitter of the upper power switch tube Tf is connected to the negative bus N, and the bridge arm Q f Upper diode D f The negative pole is connected to the positive bus P.

[0033] The power switch tube T e , T f It is a reverse blocking type switching device with reverse blocking capability but no reverse conducting capability; or it is a reverse conducting type switching device with reverse conducting capability with a diode connected in series in the forward direction of the emitter. The switching device can be a power transistor GTR, an insulated gate bipolar transistor IGBT, an integrated gate commutated thyristor IGCT, a metal oxide semiconductor field effect transistor MOSFET, such as Fig.14 The shunt inductor uses superconducting materials to reduce the loss of the shunt inductor.

[0034] The two-level power converter adopts a closed-loop control strategy to control the charging and discharging state of the arc-shaped magnet module.

[0035] Power switch tube T e Drive pulse trigger, power switch tube T e Turn on, power switch tube T f Drive pulse trigger, power switch tube T f Turn on, the arc magnet module is charged.

[0036] Power switch tube T e Drive pulse trigger, power switch tube T e Turn on, power switch tube T f Drive pulse blocked, power switch tube T f Blocking, diode D e Blocking, diode D f Turn on, the arc magnet module continues current.

[0037] Power switch tube T e Drive pulse blocked, power switch tube T e Blocking, power switch tube T f Drive pulse trigger, power switch tube T f Conducting, diode D e Conducting, diode D f Blocked, arc magnet module continues current.

[0038] Power switch tube T e Drive pulse blocked, power switch tube T e Blocking, power switch tube T fDrive pulse blocked, power switch tube T f Blocking, diode D e 、Diode D f Turn on, the arc magnet module discharges.

[0039] The arc magnet module current is controlled by closed loop, such as Fig.15 As shown in the figure, the regulator can achieve fast tracking and error-free regulation of charge and discharge currents, and maintain current balance in each module: The reference instruction is used to output the absolute value of the signal through the PI current regulator as the common reference modulation wave of each converter. D , each power switch tube is turned on and off according to the multi-level DC pulse width modulation strategy.

[0040] The phase shift control strategy is adopted between each power converter, that is, the power converter Ck, k∈{1,…,n} effectively reduces the total magnet synthetic flux ripple, reduces the magnet module induced potential and current ripple, reduces the superconducting magnet AC loss; and reduces the bus current ripple. The trigger pulse sequence of each cluster of power converters C1 and Cn is phase-shifted by 2π / n within a switching cycle T, and the trigger pulse sequence of each cluster of converter modules C1 and Cn is sequentially delayed by T / n, such as Fig.16 shown.

[0041] The invention adopts a pulse synchronization control strategy between the arc-shaped magnet modules to ensure the current balance of the magnet modules; the converter shunt inductor adopts superconducting materials to reduce the loss of the shunt inductor. The shunt inductor and the superconducting magnet are integrated into a low-temperature constant-temperature Dewar container, which can greatly reduce the leads across the environment, fundamentally avoid unnecessary lead losses, and improve the economy of superconducting application technology.

[0042] Although the present invention has been described above in conjunction with the accompanying drawings, the present invention is not limited to the above-mentioned specific embodiments, which are merely illustrative and not restrictive. Under the guidance of the present invention, ordinary technicians in this field can make many modifications without departing from the scope of protection of the present invention and the claims, all of which fall within the scope of protection of the present invention.

Claims

1. A modular energy storage system, characterized in that: The invention comprises a ring-shaped superconducting magnet formed by connecting n arc-shaped magnet modules end to end, wherein the arc of the arc-shaped magnet module is 2π / n, 2≤n≤10, each arc-shaped magnet module is connected in parallel to the busbar of the DC power grid through a DC bidirectional current source power converter, and the voltage and current of each arc-shaped magnet module are controlled to generate equal magnetic flux and superimpose in the arc direction; the power converter adopts a two-level topology, and the power switch tube T e The emitter of the diode D e The negative electrodes are connected in series, marked as connection point E, forming bridge arm Q e , power switch tube T f The collector of the diode D f The positive electrodes are connected in series, marked as connection point F, forming a bridge arm Q f , connection points E and F are connected to the two ends of the arc magnet module respectively, and the bridge arm Q e With bridge arm Q f Connected in parallel to the DC bus support capacitor C, the power switch tube T e The collector of diode D is connected to the positive bus. e The positive electrode is connected to the negative bus, the emitter of the power switch tube Tf is connected to the negative bus N, and the diode D f The negative pole is connected to the positive bus.

2. A modular energy storage system according to claim 1, characterized in that: The arc-shaped magnet module is obtained by assembling a superconducting coil (01), an inner ring (02), an outer ring (03), a radial support assembly (04), a cooling plate (05), a support side plate (06) and a current lead assembly (07) with low-temperature glue, followed by vacuum impregnation filling and curing at room temperature.

3. A modular energy storage system according to claim 2, characterized in that: The superconducting coil (01) is a double-pancake coil wound on an inner ring (02), the superconducting coil (01) and the inner ring (02) are in transitional fit, the outer ring (03) is sleeved on the outside of the superconducting coil (01) with a gap fit, the space between the outer ring (03) and the superconducting coil (01) is filled with a superconducting tape, the outer ring (03) is sleeved with a radial support assembly (04) on the outside and is in transitional fit, the cold conduction plates (05) are respectively located on both sides of the superconducting coil (01), the support side plates (06) are located outside the cold conduction plates (05), and the current lead assembly (07) is fixed on the radial support assembly (04).

4. A modular energy storage system according to claim 1, 2 or 3, characterized in that: The two-level power converter adopts a closed-loop control strategy to control the charging and discharging state of the arc-shaped magnetic module: the power switch tube T e Drive pulse trigger, power switch tube T e Turn on, power switch tube T f Drive pulse trigger, power switch tube T f Turn on, the arc magnet module is charged; the power switch tube T e Drive pulse trigger, power switch tube T e Turn on, power switch tube T f Drive pulse blocked, power switch tube T f Blocking, diode D e Blocking, diode D f Turn on, arc magnet module continues current; power switch tube T e Drive pulse blocked, power switch tube T e Blocking, power switch tube T f Drive pulse trigger, power switch tube T f Conducting, diode D e Conducting, diode D f Blocking, arc magnet module continuous current; power switch tube T e Drive pulse blocked, power switch tube T e Blocking, power switch tube T f Drive pulse blocked, power switch tube T f Blocking, diode D e 、Diode D f Turn on, the arc magnet module discharges.

5. A modular energy storage system according to claim 4, characterized in that: The arc magnet module current adopts closed-loop control, and the regulator realizes fast tracking and error-free regulation of the charge and discharge current, and maintains the current balance of each module: The reference instruction is used to output the absolute value of the signal through the PI current regulator as the common reference modulation wave of each converter. D , each power switch tube is turned on and off according to the multi-level DC pulse width modulation strategy.

6. A modular energy storage system according to claim 4, characterized in that: The power switch tube adopts a multi-level carrier phase-shift pulse width modulation strategy. By comparing multiple triangular carriers with the same amplitude and phase shift, the modulated wave is generated to control each group of power units respectively, and then superimposed to form a multi-level PWM waveform.

7. A modular energy storage system according to claim 6, characterized in that: The power converters Ck, k∈{1,…,n} adopt a phase shift control strategy. n Each cluster triggers a pulse sequence, shifting the phase by 2π / n within a switching cycle T. The converter modules C1 and C n Each cluster of trigger pulse sequences is delayed by T / n in sequence.

8. A modular energy storage system according to claim 7, characterized in that: The power switch tube T e , T f It is a reverse-resistance switching device with reverse blocking capability but no reverse conducting capability; or it is a reverse-conducting switching device with reverse conducting capability and a diode connected in series in the forward direction at the emitter.

9. A modular energy storage system according to claim 7, characterized in that: The switch device is a power transistor GTR, an insulated gate bipolar transistor IGBT, an integrated gate commutated thyristor IGCT or a metal oxide semiconductor field effect transistor MOSFET.

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